To reduce component wear and increase fuel efficiency it has long been regarded as desireable to have two wheels, generally the front wheels, of a four wheel drive vehicle be selectively engageable or disengageable from the axles by which they are driven.
Four wheel drive vehicles, which are well known and currently in wide use as utility, recreational and military vehicles, are often operated in situations in which four driving wheels are neither necessary nor desirable. In such situations, such as on good roads, the front wheel drive train can be disengaged from the transmission and, additionally, the wheel hubs themselves can be disengaged from the stub axles by which they are driven. This arrangement allows the front wheels to free-wheel relative to the stub axles and enables the drive components between the hub and the transmission to remain dormant.
Disengagement of the wheel hub from the drive axle is most often accomplished by manual movement of a lock means from an engaged to a disengaged position. Conversely, when four wheel drive again becomes desirable it is generally necessary to manually move the lock means from the disengaged to the engaged position for each wheel of a pair of wheels.
Examples of prior art devices which are manually operated and in which one member is moved axially in response to manually exerted rotary force to engage or disengage the member from a complementary member are shown in U.S. Pat. Nos. 3,184,258; 3,669,476; 3,718,213; 3,753,479 and 4,007,820.
For safety and convenience it is desireable to have the wheel hub be engageable and disengageable from the axle without the need for manual effort to be exerted at each wheel hub. Achievement of hub to axle engagement automatically, in response to driving rotation of the axle, has been conceived using roller clutches. Examples of such devices are shown in U.S. Pat. Nos. 2,884,101; 3,055,471 and 3,414,096.
Torque responsive automatic hub clutches in which a member is moved axially to engage or disengage the hub and the axle are shown in U.S. Pat. Nos. 3,217,847 and 3,656,598.
Additionally, U.S. Pat. No. 3,829,147 shows a ball and cam arrangement whereby axial movement is obtained in response to torque.
Known past automatic hub locking devices have not achieved widespread commercial success due to several factors, such as sporadic or unreliable operation, lack of durability and/or prohibitive expense of manufacture.